Worked example

The answer above is a return economy flight from London Heathrow to New York JFK for one passenger, with non-CO₂ effects included. This is how the calculator gets there:

  1. Great-circle distance from LHR (London Heathrow Airport) to JFK (John F. Kennedy International Airport): 5,540 km.
  2. No extra uplift: DESNZ's factors already include an 8% distance uplift for indirect routes and circling, so we use the great-circle distance as it isSource 2.
  3. Band: long-haul (a flight between the UK and North America). Factor for economy, with radiative forcing: 0.11704 kg CO₂e per passenger-kmSource 1 (DESNZ factor 21_316_3170_11_1).
  4. One way: 5,540 km × 0.11704 = 648 kg. Return, 1 passenger: 1,297 kg = 1.30 t CO₂e.

Without non-CO₂ effects, the same flight uses DESNZ’s CO₂-only factor and comes out lower. Switch the toggle to compare.

How we calculate

For each flight, the calculator:

  1. finds the great-circle (shortest) distance between the two airports, using their coordinates from OurAirportsSource 3;
  2. multiplies it by the DESNZ factor for the type of flight and cabin class, in kg CO₂e per passenger-kmSource 1;
  3. multiplies by the number of passengers, and by two for a return trip.

DESNZ’s factors already include an 8% uplift on the great-circle distance for indirect routes, delays and circling, so we don’t add it againSource 2.

The factors come from the UK government’s 2026 greenhouse gas conversion factorsSource 1:

Scrolls sideways to show every column.

DESNZ 2026 flight factors, kg CO₂e per passenger-km, with radiative forcing, as of June 2026
BandAverageEconomyPremiumBusinessFirst
Domestic (UK)0.23————
Short-haul, to/from UK0.130.13—0.19—
Long-haul, to/from UK0.150.120.190.340.47
International, non-UK0.140.110.170.320.44

As of Jun 2026 · Source: [1] Greenhouse gas reporting: conversion factors 2026 (flat file, version 1.2)

Scrolls sideways to show every column.

DESNZ 2026 flight factors, kg CO₂e per passenger-km, without radiative forcing, as of June 2026
BandAverageEconomyPremiumBusinessFirst
Domestic (UK)0.14————
Short-haul, to/from UK0.080.07—0.11—
Long-haul, to/from UK0.090.070.110.20.28
International, non-UK0.080.060.10.190.26

As of Jun 2026 · Source: [1] Greenhouse gas reporting: conversion factors 2026 (flat file, version 1.2)

DESNZ publishes no economy, premium or first-class factor for some types of flight. When you choose one of those cabins, the calculator uses the average-passenger factor for that type of flight and tells you so.

How flights are grouped

DESNZ groups flights by where they goSource 2:

  • Domestic: flights that start and end in the UK, including the Isle of Man and the Channel Islands.
  • Short-haul: flights between the UK and Europe or North Africa. DESNZ includes Turkey, Greenland and Gibraltar, and excludes Moldova and Ukraine.
  • Long-haul: flights between the UK and everywhere else, including Russia and the rest of Asia.
  • International: DESNZ also publishes factors for international flights between airports outside the UK.

For flights that don’t touch the UK, we use the distance. Under 3,700 km we use the short-haul factors, the cut-off DESNZ used in earlier editions. From 3,700 km we use the international factorsSource 2. Our list of European countries follows the UN regions, adjusted to the DESNZ definition.

Non-CO₂ effects (radiative forcing)

Aircraft warm the climate through more than CO₂, for example through contrails and nitrogen oxides at altitude. DESNZ recommends a multiplier of 1.7 on the CO₂ part of aviation emissions as a central estimate, and notes that the value is very uncertainSource 2. Its factors with radiative forcing already include this, so the calculator uses them directly. The toggle is on by default because it gives a fuller picture of a flight’s effect.

Limitations

An estimate, not an audit

The result uses average factors for each type of flight. Real emissions depend on the aircraft, the seating layout, how full the plane is and the route flown. DESNZ factors are for direct flights, so a journey with a connection should be entered as two flights.

Before offsetting a flight, consider whether the trip is needed, or whether a train could replace it. See our other carbon calculators for your wider footprint. Our guide to buying carbon credits as an individual covers what to check before you buy, and how to verify carbon credits shows how to confirm your credits were retired.